FishWagon

Hello all,

Well, the old 330HP 7.4 Merc went to the great anchor field in the sea...

I've decided instead of rebuilding her, to start over. This is my first marine build, and wanted a sanity check from the experts.

Here is what I am planning:

Mark IV 4bolt main block 60 over
454 Stroker Kit (I only have the cast crank/rod/pistons from old engine, and that won't do, so I might as well stroke it since I have to replace everything)

This should bring me up to a 496 if I am not mistaken.

I am going to put a set of 781 heads, having them cleaned up, mild porting, and 2.19/1.88 valves installed. (118cc chamber)

I plan on going with a set of forged pistons with the heads above, to yield a 9.5:1 compression for pump gas.

Cam I am still researching...also debating flat tappet versus roller....could use some advice here. Don't think I need to go roller. Still reading all the cam threads.

I currently have a Holly Strip Dominator intake, but plan on getting rid of it, and plan on going with Edlebrock RPM intake manifold. Will have it port matched to heads.

Still researching exhaust.

I'm not looking to go insane, just want a good, reliable engine in the 400-450hp range running at around 5k rpm. It will be hooked up to a Bravo 1 (which I am also rebuilding, or maybe source one already done). This will go in a Chaparral 2550SX to be used mostly for tubing/water sports, and of course for speed runs in fresh water lakes.

Prop to be determined.

What do you all think of this? Am I on the right track? Also, who makes a good stroker kit?


Thanks,
Rich

wjb21ndtown

I think you're on the right track. You might want to keep that intake though. You can easily get to 450-500 Hp without going crazy, and that single plain intake isn't necessarily a bad thing.

I would go hyd. roller cam, but you don't have to in order to achieve your power #'s.

jeffswav

Ok, you are on the right track so far. Have RMbuilder custom grind you a cam and prop it for 54-5500 RPM. Call him first before you buy any more parts. Do a search and you will find a lot of guys here use him. He can easily get 500HP out of a 496 stroker. I use the EMI exhaust, there a other good ones out there. Be sure to get long risers and do not try to use silent choice with the bigger cam. Get a big 3" oil cooler the one that came stock is to small. Be sure to upgrade the oiling system with bigger lines and less restrictive fittings. Be sure you get the 30psi diferential valve in the oil pad. Good luck with your build.

BillK

What the others said. Definitely hydraulic roller, and get the late model Gen6 style cam, that way you can just use the retaining plate and the Gen6 timing chain set on the front to keep the cam from walking and you dont have to mess with a cam button.

Unless the block is already .060, I would not bore it that much. If it will clean up at .030 or even .020 I would prefer to have the extra cylinder wall thickness, especially in a raw water cooled engine. You will never notice the power difference.

Bill Koustenis
Advanced Automotive Machine
Waldorf Md

stlliberator

iTrader: (1)

I got all that you need sitting in my basement that im trying to sell, I have a 4 bolt mark 4 block that has been bored 60 over, has been line honed and decked. I have a 496 forged scat crank, forged h beam scat rods, and srp 9 to 1 forged pistons. I also have a weiand dual plane high rise intake with a holly 800 (hp500) blue carb. Let me know.......

wjb21ndtown

FWIW...

If it was me building the motor, unless I had the 330 sold I would use the block, even if it is a 2 bolt main.

I agree with Billk on boring the block. Get the easy cubes from stroking, and give up the petty cubes that weaken the block. Sure, it won't be a true 496, but that only matters if your selling the motor (and that only hurts in advertising the cubes).

Griff

It sounds like you are planning on getting a new block????? Correct????
If you are, why not just buy complete 502 long block???? or even better stroke the 502??? Cost will be nearly the same.

jeffswav

I bored mine .030 over that makes a 489. If you use the Gen VI style setup you have to use a single roller not a double roller. I went through all this last year and I used a Rollmaster Double roller with a thicker alluminum cover to avoid the flex.
Like Griff said, if you are starting from scratch you could get the 502 block and go with that or build a 540. Bigger is better right.

FishWagon

I've already got the block, 4bolt 454 60 over that I had in my garage, it's a Mark IV block.

The block from the 330 was mag'd and found to have some cracks in it, so I tossed that one aside.

I do have the cast crank and rods from the stock 330hp 454 that look to be in great shape.

I would have no problem using the cast stuff in an engine like this for the street. However, my inexperience with marine builds, where a lot of time is spent in the higher rpm ranges, made me wonder if the cast items are still good enough. If I do stay that route, I would have the rods redone with ARP bolts, for me, that is cheap insurance. Obvioulsy if I keep and use the cast stuff, I'll stay 454 and just replace the pistons. If I swap out, that's what made me think of stroking it as well since I'd have to get everything anyway.

I still may stay 454 if I can reach my goals...all depends on what my research tells me.

Thanks for the input everyone, it is appreciated.

jeffswav

Depends on your budget, I have a forged stroker crank, forged hbeam rods, forged pistons. The parts list adds up in a hurry. Do not cut corners or you will just be paying for it twice when it blows up. You cannot use the crank from a Gen V in a Mark IV anway, one piece vs two piece crank seal.